The present invention relates to an optical pickup device, and in particular, to an optical pickup device which can conduct recording and/or reproducing of information for each of three or more of different optical information recording media, by using each of three light fluxes emitted from three light sources each having a different wavelength.
In recent years, there have been advanced research and development of a high density optical disc system capable of conducting recording and/or reproducing of information by using a violet semiconductor laser having a wavelength of about 400 nm. As an example, on the optical disc (hereinafter, the optical disc of this kind is referred to as “high density DVD” in the present specification) conducting recording and/or reproducing of information under the specifications of NA 0.85 and light source wavelength 405 nm, it is possible to record information with 20–30 GB per one surface for an optical disc having a diameter of 12 cm that is the same as DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB) in size.
Incidentally, if it is only possible for the optical pickup device to conduct recording and/or reproducing information properly for the high density DVD mentioned above, a value of the optical pickup device as a product is not considered to be sufficient. At present, when taking into consideration the reality that DVD and CD wherein various types of information are recorded are marketed, only recording and/or reproducing of information properly for high density DVD is not sufficient, and an arrangement to be capable of conducting recording and/or reproducing of information properly in the same way also for conventional DVD or CD owned by a user, for example, leads to enhancement of a value of a product as an optical pickup device of a compatible type. From the background of this kind, a light-converging optical system used for an optical pickup device of a compatible type is required to have power for conducting recording and/or reproducing of information properly while keeping compatibility for all of the high density DVD, conventional DVD and CD.
For attaining low cost of an optical pickup device by simplifying its structure, in this case, it is preferable originally that a light-converging optical system including an objective lens is single even for an optical pickup device having compatibility. However, aberration characteristics of an objective lens in recording and/or reproducing of information for high density DVD are required to be extremely high because of a shorter wavelength for the light source and of employment of high NA, and it is sometimes difficult to conduct recording and/or reproducing of information for DVD and CD by using the same objective lens.
With respect to high density DVD, in particular, there are actual circumstances that detailed standards are not fixed, although the wavelength to be used is roughly determined because a light source that can be used is limited. Therefore, with respect to an objective lens used for recording and/or reproducing of information for high density DVD, it is necessary to leave room for redundancy of design to a certain extent, and in this case, it is more difficult to conduct recording and/or reproducing of information properly by using the same objective lens for three or more types of optical information recording media even for DVD and CD. In contrast to this, TOKKAIHEI No. 11-296890 discloses an example of an optical pickup device that can conduct recording and/or reproducing of information for three or more types of optical information recording media by using a plurality of objective lenses.
Though it is impossible to understand clearly a type of a light-converging optical system provided in an optical pickup device, by reading drawings and descriptions, in TOKKAIHEI No. 11-296890, there is no disclosure about how to take actions for chromatic aberration caused in the case of converging a light flux emitted from a light source having a short wavelength, to say the least of it. Namely, TOKKAIHEI No. 11-296890 is one that discloses nothing about a technology capable of conducting recording and/or reproducing of information properly for three optical information recording media representing high density DVD, DVD and CD each being different in terms of information density.